This invention relates to internal combustion engines and, more particularly, to selectively altering the phasing between an engine and a fuel injector pump therefor.
Many internal combustion engines in use today, whether rotary or reciprocating, utilize fuel injection rather than carburation in view of a considerable number of advantages of the former over the latter. And, many of the fuel injection systems inject a predetermined quantity of fuel into an engine working chamber or prechamber at a particular point in an engine cycle. This, of course, requires that the fuel pump or pumps be operated in timed relation to engine speed, and thus the rotary output of the engine.
In many cases, a considerable number of gears may be employed to interconnect the engine rotary output, i.e., the crankshaft, to a rotary input for a fuel pump. As the number of gears is increased, the backlash in the system is also increased with the result that the desired timing may be increasingly difficult to achieve and poor operating efficiency will result.
In addition, in many fuel injection systems, it is desired to alter the point during the engine cycle whereat fuel is injected in accordance with some sensed operating parameter of the engine as, for example, engine speed, to maximize operating efficiency.
As a consequence of the foregoing, a number of systems have evolved whereby the phasing or timed relation between an engine mainshaft and a rotary drive for a fuel injection pump or pumps can be changed. A number of these systems require that the engine be quiescent when an adjustment be made with the consequence that achieving the adjustment which provides for maximum operating efficiency can only be accomplished through a trial and error approach.
Others do allow adjustment while the engine is operating and some even provide for adjustment in response to engine operational parameters. Typically, adjustment mechanisms of the latter categories employ facing shafts having helical splines of differing pitches on their ends. A coupling is axially shiftable on the splined ends of the shaft and dependent upon its axial position with respect thereto, advances or retards the angular position of one shaft with respect to the other.
Such constructions, while operative for their intended purpose, have accompanying drawbacks. For one, the adjustment mechanism requires a relatively long axial length and may not be usable in many cases due to space considerations. Secondly, the precision with which an adjustment can be made and maintained is in a large degree, dependent upon the accuracy utilized in machining the splines on the shafts.